Anti-dispersion is an important technical indicator to measure the quality of anti-dispersant. Hydroxypropyl methylcellulose is a water-soluble polymer compound, also known as water-soluble resin or water-soluble polymer. It is a hydrophilic polymer material that is added to the viscosity of the mixture by adding the viscosity of the stirring water. It can be dissolved in water to form a solution or dispersion. The test shows that when the content of naphthalene-based superplasticizer increases, the addition of superplasticizer will reduce the dispersion resistance of freshly mixed cement mortar. This is because the naphthalene-based superplasticizer belongs to the surface active agent. When the superplasticizer is added to the mortar, the superplasticizer is oriented on the surface of the cement particles so that the surface of the cement particles has the same electric charge. This electric repulsion makes the cement particles The formed flocculation structure is dismantled and the water wrapped in the structure is released, resulting in the loss of a part of the cement. At the same time, it was found that with the addition of HPMC content, the disintegration resistance of freshly mixed cement mortar became better and better.
1. The addition of HPMC has an obvious retarding effect on the mortar mixture. With the addition of HPMC content, the coagulation time of the mortar is successively prolonged. Under the same HPMC content, the mortar formed under water is better than that formed in the air. The cohesion time is longer. This feature is advantageous for underwater concrete pumping.
2. The freshly mixed cement mortar mixed with hydroxypropyl methyl cellulose has a good cohesive function, and there is almost no bleeding phenomenon.
3. The content of HPMC and the water demand of mortar are first decreased and then increased obviously.
4. The addition of water reducing agent improves the problem of increasing water demand of mortar, but its content must be controlled reasonably, otherwise the underwater dispersion resistance of freshly mixed cement mortar will sometimes decrease.
5. There is little difference in structure between the cement paste specimens mixed with HPMC and the blank specimens. The structure and compactness of the cement paste specimens poured in water and in the air are not much different. The specimens molded under water for 28d were slightly crispy. The main reason is the participation of HPMC, which greatly reduces the loss and dispersion of cement when pouring in water, but also reduces the compactness of cement stone. In the project, the content of HPMC should be reduced as much as possible under the circumstance of ensuring that the water does not disperse.
6. Adding HPMC underwater non-dispersible concrete admixture, controlling the dosage well is beneficial to the strength. The pilot project shows that the strength ratio of concrete formed in water to that formed in air is 84.8%, which has a significant effect.